What happened
On 1 July 2002, at approximately 21:35:32 hrs, a Tupolev TU-154M operating a charter flight from Moscow-Domodedovo to Barcelona and a Boeing B757-200 performing a cargo flight from Bergamo to Brussels collided in the night sky near Ueberlingen, Germany. The collision took place at an altitude of 34,890 ft. Both aircraft impacted the ground north of the town, causing the deaths of all 69 individuals aboard the Tupolev (60 passengers and 9 crew) and the 2 pilots aboard the Boeing.
Prior to the impact, the crew of the Boeing B7/57-200 received a Traffic Advisory (TA) followed by a Resolution Advisory (RA) from the TCAS, instructing them to descend. In response to the RA, the crew initiated a descent, which eventually reached a rate of approximately 2600 ft/min. Simultaneously, the crew of the Tupolev TU-154M received a Traffic Advisory and a subsequent instruction from Air Traffic Control to expedite a descent to FL 350 due to conflicting traffic. However, the Tupolev TU-154M crew received a TCAS Resolution Advisory to climb. This led to a critical conflict in maneuvering, as the Boeing crew was descending while the Tupolev crew attempted to climb, ultimately resulting in the mid-air impact.
Findings
Investigations into the flight data recorders and cockpit voice recorders revealed that the primary cause of the accident was the conflicting vertical maneuvers performed by the two flight crews in response to different instructions. While the Boeing B757-200 crew followed a TCAS instruction to descend, the Tupolev TU-154M crew attempted to follow a TCAS instruction to climb, even as air traffic controllers were instructing them to descend to avoid traffic.